1. Field of the Invention
The present invention relates to a variable compression ratio device. More particularly, the present invention relates to variable compression ratio device that varies the compression ratio of gas mixture in a combustion chamber in accordance with the driving conditions.
2. Description of Related Art
In general, thermal efficiency of a heat engine increases with the increase of a compression ratio, while thermal efficiency of a spark ignition engine increases when ignition timing is advanced to a predetermined level. However, the spark ignition engine makes abnormal combustion when the ignition timing is advanced at a high compression ratio and the engine may be damaged, such that the advanced angle of ignition timing is limited and the output may be reduced.
A variable compression ratio device is a device that varies the compression ratio of gas mixture, in accordance with operation conditions. With the variable compression ratio device, it is possible to improve fuel efficiency by increasing the compression ratio of gas mixture under a low-load condition of an engine, and prevent knocking and improve engine output by reducing the compression ratio of gas mixture under a high-load condition of the engine.
In order to achieve the variable compression ratio, there has been known a method of forming an oil chamber inside an eccentric ring disposed in a small end of a connecting rod and eccentrically rotating the eccentric ring by using hydraulic pressure generated by supplying oil into the oil chamber; however, in a variable compression ratio device according to the related art, it is required to increase pressure to maintain the position of the eccentric ring in the oil chamber when explosion pressure is applied, because the distance from the eccentric ring to the center of the oil chamber, such that the compression ratio is not maintained.
Further, it may be required to considerably increase oil pressure for varying the compression ratio.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.